MicroElectroMechanical System (MEMS) devices include microphones and speakers to mention two examples. In the case of a MEMS microphone, sound energy enters through a sound port and vibrates a diaphragm. This action creates a corresponding change in electrical potential (voltage) between the diaphragm and a back plate disposed near the diaphragm. This voltage represents the sound energy that has been received. Typically, the voltage is then transmitted to an electric circuit (e.g., an integrated circuit such as an application specific integrated circuit (ASIC)). Further processing of the signal may be performed by the electrical circuit. For instance, amplification or filtering functions may be performed on the signal at the integrated circuit.
The internal devices (e.g., integrated circuit, MEMS device) of a microphone are disposed within a housing or assembly. For example, these devices may be attached to a base and covered with a lid. In other words, a cavity is formed by the lid and the internal devices (e.g., an integrated circuit, MEMS device) are disposed on the base within the cavity.
In many examples, the lid is coupled to the base of the acoustic device with solder. In fact, the lid may be attached to the base by solder on both on the inside portion (in the cavity and exposed to the MEMS device and the integrated circuit) and on the exterior of the device (exposed to the external environment).
In order that the solder can be attached to the lid (and thus make the connection to the base), the entire lid is typically plated in gold (or some other appropriate metal) and then the attachment between the lid and base is made. However, in many situations after the attachment is made the device (including the solder) is re-heated. In these circumstances, the solder will melt and continues to interact with the plating, and “creeps” up the lid or flows. As this happens within the cavity, some solder can be discharged from the lid and cause failure to the MEMS device or integrated circuit within the cavity. On the outside of the lid, the “creeping” solder can continue to flow up the lid onto the surface of the lid and this will interfere with subsequent gasketing of the microphone.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.